• Proceedings of the KIEE Conference
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• 2008.04b
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• pp.176-178
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• 2008

최근 전력전자 기기와 같은 비선형 부하의 증가로 계통에서 고조파 발생 가능성은 점점 높아지는 추세이다 이러한 계통의 고조파는 부하 설비 중 누전차단기 오동작 및 과부하 등의 원인이 되므로 전기설비 안전 측면에서 중요하게 다루어질 필요가 있다. 고조파에 대한 해결책으로는 수동필터 및 능동전력필터를 들 수 있는데 본 연구에서는 기존의 3상 풀브리지 스위칭 회로를 이용한 능동필터에 비해 안정성 및 대용량 시스템 구성에 유리한 모듈형 능동 전력 필터를 제안하였다.

• The Transactions of the Korean Institute of Power Electronics
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• v.7 no.1
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• pp.101-110
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• 2002

A method to control the inverter output voltage lineally in over modulation mode of the third harmonics injected PWM inverter is proposed. The third harmonics injected PWM has a extended linear region compared with the sine PWM. But it still has a maximum voltage about 90% compared with the six step inverter. Therefore, to control the output voltage linearly in over modulation mode, analyzing the relationship between the modulation index and the peak of the fundamental component of the modified reference voltage, we can settle the problem in over modulation mode without iteration. Then we can increase the maximum fundamental component of the third harmonics injected PWM inverter comparative to six-step inverter continuously in over modulation mode. The simulation results of the inverter-induction motor system shows the validity of this method and experimental results prove it.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.47 no.10
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• pp.8-16
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• 2010

An orthogonal frequency division multiplexing (OFDM) system is a special case of multicarrier transmission, where a single data stream is transmitted over a number of lower-rate subcarriers. One of the main reasons to use OFDM is to increase robustness against frequency-selective fading or narrowband interference. However, in the radio systems the distortion introduced by high power amplifiers (HPA's) such as traveling wave tube amplifier (TWTA) considered in this paper, is also critical. Since the signal amplitude of the OFDM system is Rayleigh-distributed, the performance of the OFDM system is significantly degraded by the nonlinearity of the HPA in the OFDM transmitter. In this paper, we propose a simplicial canonical piecewise-linear (SCPWL) model based digital predistorter to compensate for nonlinear distortion introduced by an HPA in an OFDM system. Computer simulation is carried on an OFDM system under additive white Gaussian noise (AWGN) channels with 16-QAM and 64-QAM modulation schemes and modulator/demodulator implemented with 1024-point FFT/IFFT. The simulation results demonstrate that the proposed predistorter achieves significant performance improvement by effectively compensating for the nonlinearity introduced by the HPA.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.29 no.6
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• pp.369-381
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• 2017

It has been presumed that highly nonlinear skewed waves frequently observed in a surf zone could significantly influence the transmission behaviour via a porous wave breaker due to its larger inertia force than its nonlinear counterparts of zero skewness [Cnoidal waves]. In this study, in order to confirm this perception, a numerical simulation has been implemented for 6 waves the skewness of that range from 1.02 to 1.032. A numerical simulation are based on the Tool Box called as the ihFoam that has its roots on the OpenFoam. Skewed waves are guided by the shoal of 1:30 slope, and the flow in the porous media are analyzed by adding the additional damping term into the RANS (Reynolds Averaged Navier-Stokes equation). Numerical results show that the highly nonlinear skewed waves are of higher transmitted ratio than its counterparts due to its stronger inertia force. In this study, in order to see whether or not the damping at the porous structure has an effect on the wave celerity, we also derived the dispersive relationships of Nonlinear Shallow Water Eq. [NSW] with damping at the porous structure being accounted. The newly derived dispersive relationships shows that the phase lag between the damping friction and the free surface elevation due to waves significantly influence the wave celerity.

• Proceedings of the Acoustical Society of Korea Conference
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• spring
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• pp.365-368
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• 2000

자왜 재료는 자계 포화 이하에서 비선형 특성을 갖는다고 알려져 있다. 그러나 지금까지 비선형 특성을 표현하는 자왜 재료의 구조 방정식을 유도한 사례는 전무한 실정이다 본 연구에서는 자계 포화 이하에서 비선형 특성을 갖는 자왜 재료의 비선형 구조 관계식을 유도하였다. 나아가 유도된 구조 관계식을 이용하여 자왜 재료 내의 파동 방정식을 정식화하였다. 그리고 비선형 특성을 갖는 자왜 재료에서 평면파가 자계 방향을 따라 전파될 때 이방성 자왜 재료를 등방성 재료로 가정하여 종파와 횡파 속도를 구하였다.

• Journal of the Society of Naval Architects of Korea
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• v.37 no.2
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• pp.1-13
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• 2000

In the present paper, an infinite-depth unified theory is applied to the computation of the linear and second-order hydrodynamic forces on slender bodies. No forward speed is assumed, which is valid for some types of ships, like FPSOs and shuttle tankers. Strip theory solution, which is essential for the extension to theory is extended to unified theory, was obtained using NIIRD program developed at MIT. The linear theory is extended to the computation of the second-order mean-drift forces and moment. Furthermore, Aranha's formular is applied to the prediction of wave drift damping coefficients. From this study, it is proved that unified theory provides an accuracy comparable with 3D panel method for the second-order forces as well as the linear solution with much less computational effort.

• Proceedings of the Optical Society of Korea Conference
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• 1998.08a
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• pp.240-241
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• 1998

• Proceedings of the Optical Society of Korea Conference
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• 1996.09a
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• pp.61-61
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• 1996

• The Optical Journal
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• s.173
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• pp.63-68
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• 2019

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.16 no.12 s.103
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• pp.1239-1245
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• 2005

In this paper, a new predistortion linearizer using second harmonic components feedforwarding is proposed. The harmonic generator of the proposed predistorter that consists of a small signal amplifier extracts second harmonic signals. A vector modulator that modulate fundamental signal with second harmonic signals, generates the inverse third order intermodulation distortion signals and controls amplitude/phase of them with modulation factors. As a result, this linearizer is suppressed IMD3 signals of power amplifier effectively. The test results show that the third order IMD of power amplifier is suppressed more than 20 dB for CW two-tone signals. Also, it's improved the adjacent channel power ratio(ACPR) more than 5 dB for CDMA(IS-95) 4FA signals.